Hi all,
We will be using our newly acquired 2002 E350 7.3L as a tow vehicle for our 34' Airstream and I'm in the process of getting it set up.
As this vehicle used to be an Ambulance Van there are some wiring challenges I'm going to need to sort thru.

I've searched underneath the rear passenger frame rail of the van and I can't locate any trailer wiring from the factory which leads me to believe its been terminated somewhere up front when they did the conversion.
Here is my under hood fuse panel:


According to the wiring schematic the factory Tow Package with relays for the trailer battery, back up, turn and running lights are all present. (22,14,C,D)

I found two mystery plugs underneath the driver's side behind the parking break. I think one of them is for a Brake Controller but I'm not sure which is which.

This brown plug has 5 pins with the following color wires:
Black
Brown
Green
Light Blue
Dark Blue




And this gray plug has 6 pins with the following color wires:
Yellow
Orange
White with Blue stripe
Green with White stripe
Blue
Gray with Red stripe



Does anyone have any idea what these two plugs are for?
And does anyone have any experience on where I should look for the wires heading towards the rear of the van?

Thanks!

 

Not sure where you would find the wires headed to the back - if they were even installed since this vehicle had been purpose-built as an ambulance. They may have used those connections to wire into the ambulance wiring and they may not do what you expect them to now. Someone will need to chime in on this.

As for the wire harnesses under your dash, I THINK the black one is the one you'll need for a brake controller - it's been a while since I got under the dash of such an old vehicle. There is a sure-fire way to check, though - whatever aftermarket brake controller you buy will need an adapter harness to interface it with your van's harness, so if you buy the correct adapter harness, the plug on the end will match one of the empty receptacles under your dash.

 

Thanks for the reply 99powerstrokedF250.

I believe Leader is the name of the company that re-fitted this Ambo. They've added all their own relays and their wires are labeled so I should be able to trace stock and aftermarket pretty easily.
And I think you're right with the brown plug as the color codes of the wires seem to match other posts I've read here.
I wonder if the gray plug is where the wiring to the back starts..

 

Thanks for the reply 99powerstrokedF250.

I believe Leader is the name of the company that re-fitted this Ambo. They've added all their own relays and their wires are labeled so I should be able to trace stock and aftermarket pretty easily.
And I think you're right with the brown plug as the color codes of the wires seem to match other posts I've read here.
I wonder if the gray plug is where the wiring to the back starts..

 

Its the black plug. As stated, you'll need an adapter from the controller of your choice to the plug. The wiring should be present back to the bumper from the black plug, you just have to look under there and find the plug to the trailer up in the frame, It will need a short harness to the 7-pin plug that you can harvest from a superduty in the junkyard.

 

Here are the trailer wiring diagrams for a 2002 e350.

 

Thank you very much Franklin2.
I actually bought a book of the specific Wiring Diagrams for the 2002 E-Series on Ebay and its been helpful but I struggle with some of the schematics and how to translate them into what I'm seeing.
Below is the page where I located the Gray plug. On the far right is C238 ("c" stands for connection) I've done some testing with my trusty voltmeter and found the following:

Gray Plug C238:
Light Green/White Stripe and White/Blue Stripe are my turn signals.
Orange is the Trailer Battery Charge
Dark Blue is the Trailer Brakes
Yellow is is a constant 12v.. running lights?
Gray/Red is unknown.. I thought it would be reverse but I get nothing when I put the vehicle in reverse when running.

I also located C328 (bottom of page on the right) and it terminates under the driver's seat but according to this schematic is looks like its the same Orange that I'm seeing at the Gray plug?



I'm going to make my own harness loom and run it back to a 7 pin plug I'll purchase from Etrailer but I'm stumped on which wires are the Ground, Reverse and Running Lights.
Anyone have a an idea?

 

"C" means connector. "S" means splice. This attached diagram shows the origin of the trailer parking lamp circuit and relay, and the trailer reversing light circuit and relay. They leave this diagram on "E", "F", "G" and "H".

 

This diagram shows that "E", "F", "G" and "H" go to the rear to the taillights directly. I do not see a separate harness for these circuits, they must have used the trailer tow circuits for the rear lights. You could verify this by pulling the trailer tow parking and reversing lamp relays and see if the rear lights fail to function with these relays out.

 

Fantastic idea Franklin2.

Its dark and I'm just getting home after a long crazy shift, but I will dive into this tomorrow and report back.
Thanks for the help.

 

If you say your ambulance "van did come did come with a tow package" (Ford says otherwise) and that you are "using a Tekonsha P3", then where did you plug the P3 in when you were using it?

 

Frankin2,
I pulled the relays for the parking and reverse lights but when I turned the van on and put it in reverse I still had reverse and park lights. The relays are C and D and are the white ones in the first picture.

Blast, I thought we were on to something there. I didn't pay much attention to that particular schematic as it was labeled for the 550 and I didn't think it would apply to my 350 but it makes sense as this was considered a "Stripped Chassis". I have power going to the relays because when the headlight switch is on I can hear them click when I plug them back in.

Any reason I can't splice the off the back up alarm and run this to the trailer?
Also, when I tested the Dark Blue brake wire it doesn't read any voltage when I apply the brake pedal. But I do get 12v at the Brown plug for the Brake Controller when I step on the pedal..